Synthetic detergent bars, frequently referred to as syndet bars, are well known and are becoming increasingly popular. However, wide spread replacement of soap bars by syndet bars has not so far been possible for a variety of reasons, primarily the poor physical characteristics of syndet bars as compared to soap bars.
Major drawbacks of conventional soap bars for use such as toilet bars include:
(a) The efficacy of soap in regard to detergency and lathering is seriously impaired in hard water due to precipitation of the calcium and magnesium salts of soaps.
(b) In hard water areas precipitated calcium and magnesium salts of soaps adhere to and build up on sinks, bathtubs, etc. giving rise to undesirable "soap ring." The hard water soaps also adhere to the skin and give an uneasy, sticky, dirty feeling.
(c) Soap has an alkaline pH which is somewhat irritating to skin and eyes.
Many synthetic detergents are known which are free from the above deficiencies of soap but despite this, synthetic detergents have not found any appreciable to overwhelmingly dominate this market. The reason for this is that soap has physical properties which make it ideally suited for toilet bars and which cannot be easily duplicated using synthetic detergents.
Synthetic detergents do not possess the physical properties of soap, thus making them unsuitable for forming into a shaped toilet bar as is done with soap. This problem is overcome by blending synthetic detergents with a binder system in an effort to formulate a mass with physical properties more like soap to enable it to be formed into bars. Ingredients generally constituting binder systems are water soluble fatty acids, fatty alcohols, mono-, di-, or triglycerides, fatty acid esters, particularly fatty acid esters with fatty alcohols, lanolin, petrolatum, etc. are suitable preferably melting at 30.degree. to 90.degree. C. Utilization of binder systems of this type results in forming of a synthetic detergent bar with physical properties which are a poor match for soap and having the disadvantages previously disclosed.
Among the physical deficiencies commonly encountered with previously known syndet bars are the following:
(1) Syndet bar masses are generally not efficiently processed into bars with conventional soap bar processing equipment. Bar extrusion is often difficult and much slower in extrusion rate. The cut bars are not easily stamped as they stick to the stamping molds requiring use of refrigerated molds and/or special release agents and techniques. The shape of the bars are often limited to rectangular shapes as the syndet bar is not sufficiently plastic to be formed into highly curved shapes without cracking. Syndet bars tend to have a dry texture with a rough or sandy feel when used. These and other problems occur because the formulated syndet bars do not possess the amorphous, microcrystalline structure of soap and soap's resulting plastic properties and smooth, pleasant texture.
(2) Synthetic detergents useful for syndet bars are more water soluble than soap resulting in rapid wear rate and tending to dissolve more in wet soap dishes than does soap.
Descriptions of typical syndet bars suggested by the Prior Art are included for instance in U.S. Pat. Nos. 2,781,321, 2,894,912 and 3,862,965.
It is desirable to prepare a syndet bar mass whose physical properties are virtually identical to soap enabling it to be processed into bars by exactly the same procedures normally used with soap to yield a syndet toilet bar whose appearance, texture, smooth feel and plasticity are virtually identical to and indistinguishable from soap bars. Such a bar should also have a wear rate similar to soap and dissolve in water to an extent similar to soap when left in a wet soap dish.